She asked the children on the video call with her, "if a friend of yours is really kind to you, how does that make you feel?"
The Duchess has long promoted the benefits of spending time outdoors and said: "It's come up in so many different conversations whether it's food, volunteering, and in all the mental health work that we've been doing, about how everyone is benefitting from being outside".
Kate Middleton has addressed the "frustrations" of being in lockdown, while encouraging school students to share their problems and be kind to people. Sometimes these feelings may be good, but sometimes they may be uncomfortable, and we feel anxious, angry or upset.
On a personal note, she added: "It's been a really hard time for us all".
"As we help others, we mustn't forget to nurture ourselves by taking the time to focus on the things that make us feel happy too", she added. This might be playing our favourite game, being outside, or talking to our friends.
Kate Middleton delighted children across the United Kingdom by making a surprise appearance in an online school assembly for the Oak National Academy, an online classroom set up to support teachers and parents during the coronavirus pandemic.
The adorable photographs were shared to the Kensington Palace social media pages and are the latest to be taken by the Duchess of Cambridge.
Oak National Academy was created in response to the lockdown, supporting teachers educating their pupils remotely, and since its launch has delivered over 12 million lessons to children and young people.
Students across Britain welcomed a very special guest for their morning assembly yesterday: the Duchess of Cambridge herself. They all help with our mental wellbeing.
The Duchess has regularly campaigned for better support for young people's mental health, and is an ambassador for Place2Be.